A Radio Frequency (RF) measurement system is one that measures something about a Device Under Test (DUT) by sampling and measuring signals applied to and coming from the DUT. A vector measurement system will measure both magnitude and phase information, while a scalar measurement system will measure magnitude only.
A “signal analyzer” measures properties of a signal relative to itself, such as magnitude or phase vs. frequency or time. A “network analyzer” measures properties of a signal at a specific reference plane, so that many of the measured signal properties can be related to characteristics of the DUT itself.
In this document, a “tuner system” will refer to a RF measurement system which uses some kind of tuner or tuners to control impedance seen by the DUT.
An “automated tuner” may be computer controlled; a “manual tuner” is controlled manually by the user.
A “passive tuner” controls the impedance seen by the DUT by changing hardware settings which affect the passive reflection. The maximum reflection is limited by the physical hardware and losses between the tuner and the DUT.
An “active tuner” controls the impedance seen by the DUT by feeding a signal back into the DUT with a specific magnitude and phase relative to the signal from the DUT. The impedance seen by the DUT will result from a combination of the passive reflections in the circuit and the “active” signal fed back to the DUT. In principle, the maximum effective reflection can be up to or even greater than unity. In practice, this is limited by the amount of power generated by the measurement system that can be fed back to the DUT to synthesize that impedance.